Bonus:
You can modify the output of "tc.path" to get back only a part of that string.
(Open "Files > Multi-Rename Tool..." and there the help (press F1-key) for the syntax)
For example from MRT-Help: "[N2-5] Characters 2 to 5 from the old name..."
you would use that in Custom column like "[=tc.path:2-5]"

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Extra Bonus:
There are "Content plugins" (WDX) which can execute user written scripts,
and there result/output you can use as Custom column.